Laminectomy alone vs laminectomy with posterior fusion in lumbar spinal stenosis: The role of instability

Table 1 Summary of the contributors to lumbar spinal instability in the context of lumbar spinal stenosis

Cause of instability	Imaging findings	Impact on stability	Surgical implications
Degenerative spondylolisthesis	Anterolisthesis of vertebral body; facet joint effusion (> 1.5-2 mm)	Abnormal translation; facet capsule laxity	May be considered for fusion if instability is demonstrable; decompression alone may risk progression of slip
Facet joint degeneration	Hypertrophy, joint space narrowing, subchondral sclerosis, osteophytes	Loss of posterior element constraint; possible capsular laxity	Preserve > 50% of facet during decompression to reduce risk of iatrogenic instability
LF thickening and buckling	LF buckles into canal; often secondary to facet arthropathy and loss of posterior tension	Contributes to stenosis; not a primary instability cause, rather a correlator	LF removal is part of decompression; does not necessitate fusion unless other instability indicators are present
Intervertebral disc degeneration	Disc height loss; Modic changes; vacuum phenomenon	Load shift posteriorly; increased facet strain	May predispose to instability after decompression; fusion only in combination with other signs
PLC laxity	Disruption or thinning of supraspinous/interspinous ligaments (MRI)	Reduced posterior tension band stability	If ≥ 2 spinal columns compromised, fusion is often considered, but thresholds and definitions vary
Iatrogenic resection	Postoperative facet removal > 50%	Immediate segmental hypermobility	High risk of postoperative instability; may require fusion during index surgery depending on stability assessment

LF: Ligamentum flavum; PLC: Posterior ligamentous complex; MRI: Magnetic resonance imaging.